This invention relates to systems and methods for increasing the brightness of illumination systems, particularly for an illumination system and method that recycles light emitted from a light source in order to increase the brightness of that light source.
Light sources are used in all types of illumination applications. Typical light sources include but are not limited to arc lamps, halogens, fluorescent devices, microwave lamps, and Light Emitting Diodes (LEDs). Many applications require an illumination system with a high level of brightness in a small effective emitting area. This high level of brightness can be accomplished conventionally by adding more light sources. However, this can be both technologically impossible if there is a limited space for integrating light sources and economically unfeasible as it can be expensive to integrate and use multiple light sources. Accordingly, the present invention proceeds upon the desirability of increasing the brightness of a light source without increasing the number of the light source.
For example, microdisplay based television (MDTV) has the potential of being low cost with large screen size. Traditional MDTVs are usually illuminated by arc lamps. Although this light source is the brightest at the lowest cost, the need to split the white light into 3 colors and the short lifetime make it less desirable. With advances in LED technology, the use of LED as the light source in MDTVs has to be considered to capture the long life feature of LEDs and other benefits such as instant ON. However, at the present time, LEDs are not bright enough for low cost application using small imaging panels or with larger screens. LED recycling scheme has been used to enhance the brightness of the light source, see U.S. Pat. No. 6,869,206 issued to Zimmerman et al. However, Zimmerman et al. describes enclosing the LEDs in a light-reflecting cavity with one light output aperture. Also, U.S. Pat. No. 6,144,536 issued to Zimmerman et al. describes a fluorescent lamp having a glass envelope with a phosphor coating enclosing a gas filled hollow interior. A portion of the light generated by the phosphor coating is recycled back to the phosphor coating. The present invention proceeds upon the desirability of providing a recycling device that can be coupled to one or more LEDs to increase the useable brightness of the LED by recycling efficiently such that smaller panels can be used or large screens can be illuminated with sufficient brightness.
For example, LEDs are one type of light source used in many illumination applications such as general lighting, architectural lighting, and more recently in projection televisions. When used in projection televisions for example, LEDs must emit light in a small effective emitting area at a high brightness level in order to provide the requisite high light output on the television screen. Specifically, the LEDs must provide an intense and bright light as measured in lumens at a small and solid angle in a small emitting area to be useful in projection televisions. Unfortunately, the currently available LEDs are not bright enough to be useful in illuminating large projection television screens, which are increasingly popular with the consumer.
Therefore, there is a need for a method and system for increasing the brightness of LEDs so as to provide an illumination system that meets the demands of the current and future applications at a reasonable cost.